Our overall objectives are to study immunoregulatory T cell interactions in patients with B-cell CLL andto investigate T lymphocyte-autologous leukemic cell interactions inpatients with acute leukemias. We propoe: 1. To investigate if defective helper T cell function or excessive suppressor T cell activity is present in patients with CLL, using purified populations of T4-positive (helper) and T8-positive (suppressor) cells. To examine the radiosensitivity of helper and suppressor T cells in CLL and to investigate T-T cell immunoregulatory interactions (T8-suppressor T4-helper) in these patients. To determine whether abnormal helper or suppressor function is associated with hypogammaglobulinemia or clinical course of patients with CLL. 2. To establish whether autologous T4-positive inducer cells are needed for the optimal generation of allospecific cytotoxic responses, by purified t8-positive cells from patients with CLL. 3. To study cell interactions between remission T lymphocytes and autologous leukemic cells from patients with acute lymphoblastic and myelogenous leukemia during generation of "autologous leukemia specific cel mediated cytotoxicity", in "three-cell" type mixed lymphocyte cultures. Specifically we will determine: (a) the phenotypes of the (1) lymphocyte subpopulations exhibiting proliferative and cytotoxic responses to autologous leukemic cells (ii) cytotoxic effector cells, using monoclonal antibodies. (b) if T4-inducer cells are required for optimal generation of cytotoxicity. (c) the effect of non-polymorphic anti-DR monoclonal antibodies and of polymorphic anti-DR reagents (and their F(ab')2 fragments) on the proliferative and cytotoxic responses in the absence of complement. (d) whether exogeneously added I1-2 can replace the requirement for "third-party" allogeneic stimulating cells.